How do you use "て形+ある"?
How do you use "て形+ある"?

例えば、「窓が開いている」 - The window is open. (no agent or reason implied).
「窓が開けてある」 - The window is open (because someone opened it).

Please give me other examples.

Thank you.

Question

How do you use "て形+ある"?
How do you use "て形+ある"?

例えば、「窓が開いている」 -> The window is open. (no agent or reason implied).
「窓が開けてある」 -> The window is open (because someone opened it).

Please give me other examples.

Thank you.

Answer

The first sentences don't mention about the person who does it, and the second ones should have the person who does that.

本がおいてある。(There is a book.) 
本を置いておく。(There is a book, someone puts a book.)

昼ごはん(ランチ)が作ってある / できている。(The lunch is ready, prerared, cooked.) 
昼ごはん(ランチ)を作っておく。(The lunch is ready, prepared, cooked, someone does that.)

テレビがついている。(TV is on.) 
テレビをつけておく。(TV is on, someone turns on.)

I hope my English isn't bad and this helps you.

Answer

More examples here:
http://www.guidetojapanese.org/learn/grammar/teform

To sum up:
～ている = enduring state (like continous tense in English)
～てある = resultant state
～ておく = preparation for the future